An exciting new area in neurodegenerative disease research is the emerging phenomenon of prion-like spreading of neurodegenerative disease proteins. Prions are well established as the protein-based infectious agent underlying the spongioform encephalopathies. In these rare, albeit devastating, diseases the prion protein converts from the normal soluble form to the aggregated self-templating infectious form. This process initiates an inexorable spread of pathology and contingent neurodegeneration throughout the brain. But could this disease mechanism extend to the more common neurodegenerative diseases like Parkinson?s disease (PD) and Alzheimer?s disease and related dementia? If so, it represents a game changer in terms of understanding disease mechanisms and opens many new avenues for therapeutic development. However, any therapeutic or mechanistic investigation into prion-like spreading will require the development of powerful new imaging approaches to track the path of prion-like spread and understand how these protein aggregates alter brain function as they spread. We will need to understand why they take some routes but not others and how this impacts brain function. To address this challenge, we have formed an interdisciplinary team, consisting of an engineer and a geneticist. First, we will use state of the art brain clearing technology to obtain high-resolution images of prion-like protein propagation of the Parkinson?s disease protein ?-synuclein. We will monitor these aggregates as they spread from one neuron to the next, tracking their paths. These high-resolution brain wide 3D maps of alpha-synuclein spreading will empower us to identify gene expression patterns associated with spreading paths and to nominate genes for functional studies. Then, we will utilize advanced high-resolution optogenetic functional magnetic resonance imaging (ofMRI) to reveal the longitudinal effects of prion-like spreading on brain network activity and likewise the impact of neural activity on prion-like spreading. Our experiments will provide fundamental mechanistic insight into prion-like spread of neurodegenerative disease. The tools we apply and the lessons we learn will likely be broadly applicable to neurodegenerative diseases including Alzheimer?s disease and related dementias.